Properly link flecs library

engine/libs/flecs/examples/cpp/systems/pipeline/src/main.cpp

@@ -0,0 +1,43 @@
+#include <pipeline.h>
+#include <iostream>
+
+struct Position { 
+    double x, y;
+};
+
+struct Velocity { 
+    double x, y;
+};
+
+int main(int, char *[]) {
+    flecs::world ecs;
+
+    // Create a system for moving an entity
+    ecs.system<Position, const Velocity>()
+        .kind(flecs::OnUpdate) // A phase orders a system in a pipeline
+        .each([](Position& p, const Velocity& v) {
+            p.x += v.x;
+            p.y += v.y;
+        });
+
+    // Create a system for printing the entity position
+    ecs.system<const Position>()
+        .kind(flecs::PostUpdate)
+        .each([](flecs::entity e, const Position& p) {
+            std::cout << e.name() << ": {" << p.x << ", " << p.y << "}\n";
+        });
+
+    // Create a few test entities for a Position, Velocity query
+    ecs.entity("e1")
+        .set<Position>({10, 20})
+        .set<Velocity>({1, 2});
+
+    ecs.entity("e2")
+        .set<Position>({10, 20})
+        .set<Velocity>({3, 4});
+
+    // Run the default pipeline. This will run all systems ordered by their
+    // phase. Systems within the same phase are ran in declaration order. This
+    // function is usually called in a loop.
+    ecs.progress();
+}